Each sensor in a sensor array may receive a copy of a signal emitted from a source. The sensor can be a suitable type of sensor such as, for example, a microphone sensor to capture sound. For example, each microphone sensor in a microphone array may receive a respective version of a sound signal emitted from a sound source at a distance from the microphone array. The microphone array may include a number of geographically arranged microphone sensors for receiving the sound signals (e.g., speech signals) and converting the sound signals into electronic signals. The electronic signals may be converted using analog-to-digital converters (ADCs) into digital signals which may be further processed by a processing device (e.g., a digital signal processor). Compared with a single microphone, the sound signals received at microphone arrays include redundancy that may be explored to calculate an estimate of the sound source to achieve noise reduction/speech enhancement, sound source separation, de-reverberation, spatial sound recording, and source localization and tracking. The processed digital signals may be packaged for transmission over communication channels or converted back to analog signals using a digital-to-analog converter (DAC).
The microphone array can be coupled to a beamformer, or directional sound signal receptor, which is configured to calculate the estimate of the sound source. The sound signal received at any microphone of the microphone array may include a noise component and a delayed component with respect to the sound signal received at a reference microphone sensor (e.g., a first microphone sensor in a microphone array). A beamformer is a spatial filter that uses the multiple copies of the sound signal received at the microphone array to identify the sound source according to certain optimization rules.
A minimum variance distortionless response (MVDR) beamformer is a type of beamformers that is obtained by minimizing the variance (or power) of noise at the beamformer while ensuring the distortionless response of the beamformer towards the direction of the desired source. The MVDR beamformer is commonly used in the context of noise reduction and speech enhancement using microphone arrays.